Field of the Invention
The present invention relates to a fuel evaporative gas emission control apparatus, and particularly to an abnormality detection technique of the fuel evaporative gas emission control apparatus.
Description of the Related Art
Conventionally, in order to prevent release of fuel evaporative gas that is evaporated in a fuel tank into the atmosphere, there has been proposed a fuel evaporative gas emission control apparatus that is configured by a canister that is interposed in a communication path that provides communication between a fuel tank and an intake passage of an internal combustion engine, a sealing valve that provides communication or blockage between the fuel tank and the canister, and a purge valve that provides communication and blockage of the communication path between the intake passage and the canister (refer to Japanese Patent No. 4107053, for example). The fuel evaporative gas emission control apparatus causes the fuel evaporative gas in the fuel tank to flow out to the canister by opening the sealing valve and closing the purge valve at a time of refueling, and causes the fuel evaporative gas to adsorb to the activated carbon that is placed in the canister. Subsequently, the fuel evaporative gas emission control apparatus opens the purge valve to discharge the fuel evaporative gas, which is caused to adsorb to the activated carbon in the canister, to the intake passage of the internal combustion engine and treats the fuel evaporative gas, at an operation time of the internal combustion engine.
Incidentally, in the fuel evaporative gas emission control apparatuses including canisters as above, there is also a fuel evaporative gas emission control apparatus that further includes a canister opening and closing valve that opens and closes the communication path and the canister. The canister opening and closing valve is used in leak monitoring of the fuel tank, the canister, the communication path and the like that configure the fuel evaporative gas emission control apparatus, for example, measures the state of change in the internal pressure of the communication path by closing the canister opening and closing valve, thereafter measures the state of change in the canister internal pressure by opening the canister opening and closing valve, and from the measurement results, determines presence or absence of leak in the communication path.
However, the leak monitoring described above cannot be carried out normally in some cases when the pressure in the fuel tank is high. For example, when the temperature of the fuel tank increases due to the high-temperature outside air during soak in which a vehicle is parked, the tank internal pressure increases and acts on the canister opening and closing valve which is being closed. Since in the state where the high tank internal pressure acts like this, a valve opening delay occurs to the canister opening and closing valve, and the canister opening and closing valve cannot be opened at a proper timing, there arises the problem that leak monitoring cannot be carried out normally.